Photoflash lamp and method



PHOTOFLASH LAMP AND METHOD Filed Sept. 26, 1963 Invavtor K T'L Sgjafr b9His lier-meg United States Patent 3,218,832 PHOTOFLASH LAMP AND METHODKarl Seidler, Augsburg, Germany, assignor to Patent-Treuhand-Gesellschaft fur elektrische Gluhlampen m.b.H.

Filed Sept. 26, 1963, Ser. No. 311,751 Claims priority, applicationGermany, Nov. 9, 1962,

P 30,539 2 Claims. (Cl. 6731) The present invention relates tophotoflash lamps having a glass envelope and a filling of combustiblematerial and oxygen and more particularly to a splinterproof protectivecoating therefor.

When a lamp is flashed, an instantaneous peak pressure is created in theenvelope and the glass envelope is brought to high temperature for ashort time. Because of the high superpressure at the moment of flashing,the glass envelope tends to break into pieces. In order to prevent thislatter or to hold together the glass splinters, the outer or inner orboth of the surfaces of the bulb are provided with a splinterproofcoating of lacquer.

In the case of well known photoflash lamps wherein the pressure of theoxygen filling does not much exceed atmospheric pressure a splinterproofcoating of cellulose acetate butyrate has been used. The lamp bulb wascoated by dipping it once into a clipping bath consisting of a solutionof cellulose acetate butyrate in a solvent and in most cases containinga softener.

In the case of miniature photoflash lamps developed recently and havingan oxygen pressure of much more than One atmosphere such a singlelacquering with cellulose acetate butyrate did not prove satisfactory.Because of a very high peak pressure and high peak temperature many ofthe lamps burst and all flashed lamps show a considerable change in thelacquer coating, such as molten places and formation of blisters. Also,at the moment of flashing there was an intense development of smoke bythe lacquer coating which has a very bad effect on the reflector surfaceof the flash device and which had a very strong smell associatedtherewith. Because of this a lacquering of cellulose acetate has beenused in miniature photoflash lamps. Sufiicient high strength may,however, be obtained with this material only by repeated lacquering,which repeated lacquering increases the cost of manufacture.Furthermore, a splinterproof coating made by repeated lacquering withcellulose acetate does not remain unchanged when flashed, but stillshows formation of blisters, molten places, and development of smoke.

It is an object of the present invention to provide a splinterprooflacquer coating which has, in the case of miniature photoflash lampswith high filling pressure, suflicient protective effect even as singlecoating and does not show any formation of blisters, molten places ordevelopment of smoke.

Therefore, in accordance with the present invention there is provided aphotoflash lamp having a glass envelope, a filling of combustiblematerial and oxygen at a pressure exceeding one atmosphere and asplinterproof lacquer coating which consists essentially of cellulosepropionate.

The accompanying drawing shows a miniature photoflash lamp with anoxygen pressure exceeding one atmosphere and coated with a splinterprooflacquer coating in accordance with the invention.

The envelope 1 of the miniature photoflash lamp is filled withcombustible material 2, e.g. with shredded zirconium foils in an oxygenatmosphere the pressure of which is higher than one atmosphere. By meansof the igniting device 3 which is in well known manner actuated by meansof the contacts 4 being taken outwards through the seal, combustion ofthe filling is brought about and, thereby, the light emission. Theenvelope is provided with a protective coating 5 consisting of a lacqueraccording to the invention which consists essentially of cellulosepropionate.

Generally, the coating is applied by dipping into a solution ofcellulose propionate. The dipping solution contains, preferably, besidea solvent also an addition of up to 10% by weight of a softener. Dibutylsebacate has proved to be especially good as the softener.

A dipping lacquer for instance is composed of by weight of a solvent,18% by weight of cellulose propionate and 2% by weight of dibutylsebacate.

The solvent for the cellulose propionate and the softener includespreferably 3 parts of a low boiling, i.e., a boiling temperature from7577 C., material such as ethyl acetate, methanol and/or ethanol, 2parts of an intermediate boiling, i.e., a boiling temperature from138152 C., material such as methyl glycol acetate and 1 part of a highboiling, i.e., a boiling temperature from -170 C., material such asdiacetone alcohol.

Thus, a very suitable dipping lacquer for obtaining, in a singledipping, suflicient splinterproof protection of the miniature photoflashlamps without any formation of blisters or any development of smoke whenthese lamps are flashed consists of 30% by weight ethyl acetate 14% byweight methanol 6% by weight ethanol 20% by weight methyl glycol acetate10% by weight diacetone alcohol 18% by weight cellulose propionate 2% byweight softener dibutyl sebacate.

The percentages of the different solvents are, suitably, chosen in sucha manner that there is obtained preferably a viscosity of 200 sec/22 C.Ford-cup 8 mm.

For lamps having an oxygen pressure of 2 to 4 atmosphere a singledipping with the splinterproof lacquer described in the presentinvention is suflicient whereas two dippings are necessary if celluloseacetate is used. In case of even higher filling pressures of the lampstwo dippings with a lacquer of cellulose propionate are suflicientwhereas, hitherto, in case of cellulose acetate 4 dippings have beennecessary.

In order to adapt the light emission of the photoflash lamps tosensitivity of, e.g., color films, a suitable coloring substance mayalso be added, if desired, to the dipping lacquer.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. A photoflash lamp comprising a glass envelope, a filling in saidenvelope of combustible material and oxy gen at a pressure exceeding oneatmosphere, and a splinterproof protective coating on the exteriorsurface of the glass envelope consisting essentially of cellulosepropionate.

3 4 2. A photoflash lamp comprising a glass envelope, 2. 2,868,6701/1959 Van Laar et al 6731 filling in said envelope of combustiblematerial and oxy- 2,927,036 3/1960 Seaver 106-181 X gen at a pressureexceeding one atmosphere, and a splin- 3,022, 53 2 19 2 Baird 7 terproofprotective coating on the exterior surface of 3 0 3 112 12/19 2 Caldwellet 1 10 131 X the glass envelope consisting essentially of cellulosepro- 5 pionate and a small amount of dibutyl sebacate plasticizer. THERREFERENCE References Cited by the Examiner Publication: Cellulosics, byW. D. Paist, 1958, ReinldPbLC .,Ch dHllLtd.,L d ,TP UNITED STATESPATENTS ho apman an a on 986 A2, p. 33, pps. 34-37 relied on. 2,510,1776/1950 Horback 106-181 10 2,673,162 3/1954 Williams et a1 106181 EDWARDMICHAEL, Primary Examiner-

1. A PHOTOFLASH LAMP COMPRISING A GLASS ENVELOPE, A FILLING IN SAIDENVELOPE OF COMBUSTIBLE MATERIAL AND OXYGEN AT A PRESSURE EXCEEDING ONEATMOSPHERE, AND A SPLINTERPROOF PROTECTIVE COUTING ON THE EXTERIORSURFACE OF THE GLASS ENVELOPE CONSISTING ESSENTIALLY OF CELLULOSEPROPIONATE.